Conceptually, a natural gas transportation system may be thought of as a network of interconnected gas pipelines which are joined at discrete locations. Additionally, there will be locations within the network where gas can be added into the system or removed from it.
Within such a gas transportation system, the constituent pipelines receive requests for gas transportation (i.e., “nominations”) from shippers who obtain gas at certain (receipt) locations along the pipeline and wish to transport it to some other (delivery) locations. While some of these requests specifically refer to actual physical locations where gas respectively enters and leaves the pipeline, a number of the requests involve logical locations within the network referred to as “pools” by those of ordinary skill in the art.
Within the context of a gas transportation network, a pool can be thought of as a booth at a trade show (or even a stall in an open-air market): pipeline customers gather their available gas at these specific locations, trade it to one another, and also submit nominations to transport gas from pools to the actual delivery points for their own customers. Since pools are just logical points on the pipeline, and not physical storage, no gas must be left in any pool at the end of the day. In other words, all of the market stalls must be emptied.
It is a primary goal of pool balancing to make certain that the sum of daily receipts into each pool is equal to the sum of daily deliveries from that pool. This goal is conventionally achieved by cutting the gas volume for some of the nominations that are involved in pooling.
Pool balancing typically involves three types of nominations: external receipts into a pool (requests to transport gas from real receipt points to pools), external deliveries (where gas is transported from pooling locations to actual delivery points), and pool-to-pool transactions (where gas is traded between pools belonging to different owners, which could also include transportation if these pools belong to locations associated with different parts of the pipeline). As an example, pool-to-pool transfers might be made for any number of reasons, but one popular reason is that such transfers provide a mechanism for pool owners that believe gas prices will go up during the month to buy extra gas on a long-term contract, or, alternatively, it allows other buyers with the opposite belief to make short-term gas purchases at the pools.
Ideally, nominations involving each individual pool should be balanced when they are submitted to the pipeline, but in reality that does not necessarily happen. For example, last-minute gas shortages or changes in demand, along with nominating discrepancies are quite common and can cause imbalances in one or more pools. In addition, physical and contractual constraints imposed by the pipeline itself frequently lead to nomination cuts, including cuts in pool external receipts and deliveries. All these factors can throw a particular pool out of balance, which typically affects pool-to-pool transfers; and, as a consequence, the whole pool system becomes unbalanced.
Those of ordinary skill in the art will recognize that the network of pool-to-pool transfers can include dozens (or, for larger pipelines, even hundreds) of pools that are directly or indirectly interconnected, which can make pool balancing a rather daunting task. For example, it is not uncommon that some of the gas transferred from pool A will go through pools B, C, D, and then back to pool A, resulting in what is known as a closed loop A→B→C→D→A. Of course, much more complex looping configurations are possible and are regularly encountered in practice.
Since pipelines make money by charging fees for gas transportation, it is to the advantage of the pipelines to achieve pool balancing by reducing the amount of transmitted gas as little as is possible. Of course, that strategy has the further favorable consequence of providing customers with a greater percentage of their gas request as well. Those of ordinary skill in the art will recognize that a strict set of rules must be followed when cutting nominations, rules which stem from the interlocking system of priorities assigned to the nominations by the pool owner (and possibly by other parties). If either incoming or outgoing nominations need to be cut to balance a pool, these priorities will determine the cut order for individual nominations.
Heretofore, pool balancing software programs have solved the above-described problem by sequentially balancing one pool at a time, e.g., by cutting the pooling nominations on either the receipt or the delivery side of each pool. These cuts are then taken into account when the next pool is analyzed, and so on, until all the pools have been examined. Of course, at the end of the first pass through the pools some of the previously balanced pools will likely have become unbalanced again (if, for example, a pool-to-pool transaction from Pool No. 25 to Pool No. 3 has been cut to balance Pool No. 25, then Pool No. 3 is now out of balance). So, a conventional pool balancing system will likely require several passes through the entire pool system, with the method continuing until a clean pass with no additional cuts is achieved. In practice, hundreds or even thousands of passes may be needed—if for no other reason because of the presence of closed loops—with resulting excessive cuts in the gas volumes.
Thus, what is needed is a method of gas pool balancing that provides an accurate and rapid determination of the cuts necessary to balance an entire network of pipelines and pools. Further, the method should reach a solution with relatively few passes through the system, thereby conserving computing resources and reducing the magnitude of rounding and other numerical errors.
Heretofore, as is well known in the gas transportation and trading arts, there has been a need for an invention to address and solve the above-described problems. Accordingly, it should now be recognized, as was recognized by the present inventor, that there exists, and has existed for some time, a very real need for a method of pool balancing that addresses and solves the above-described problems.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.